1. Field of the Invention
The present invention relates to a developer bearing member for visualizing a latent image using a developer including a toner. In addition, the present invention also relates to a developing device using the developer bearing member, and a process cartridge and an image forming apparatus using the developing device.
2. Discussion of the Background
Recently, copiers and printers are required to produce high quality images while having a good combination of reliability and stability. In order to satisfy such requirements, it is preferable to form a uniform developer layer on the peripheral surface of the developer bearing member, which is used for developing a latent image, over a long period of time. Therefore, developing rollers, the surface of which is roughened by sandblasting or has plural V-form grooves extending in a direction parallel to the rotation axis of the developing rollers, have been typically used for conventional developer bearing members.
When the roughness of the sandblasted surface of the developing rollers is too small, the developing rollers have poor developer bearing ability. When the roughness of the surface of the developing rollers is increased to improve the developer bearing ability thereof, a problem which occurs is that the developer bearing rollers are deformed in the manufacturing process.
The developing rollers having plural V-form grooves extending in a direction parallel to the rotation axis thereof have a drawback in that a large amount of stress is applied to the developer on the surface of the developing rollers when (the edge of) each of the plural grooves passes above (or below) a developer layer forming member. This is because each of the grooves is parallel to the developer layer thickness controlling member and therefore the entire portion of each of the plural grooves passes above (or below) the developer layer thickness controlling member at the same time. In addition, the developing rollers having plural V-form grooves have another drawback in that the amount of developer in the peripheral direction (i.e., the rotation direction) of the developing rollers varies when the shapes (such as depth) of the grooves vary, resulting in formation of uneven density images.
In attempting to remedy the drawbacks of the developing rollers having plural V-form grooves extending in a direction parallel to the rotation axis thereof, published unexamined Japanese patent applications Nos. 2003-316146, 2003-208012, 2000-242073 and 07-13410 have disclosed developing rollers, the surface of which has plural grooves which are slanting relative to the direction parallel to the rotation axis thereof.
When such slanting grooves are formed on the surface of a developing roller, a problem in that the developer bearing ability of the developing roller deteriorates after long repeated use occurs depending on the conditions of the slanting grooves. In this case, the degree of deterioration of the developer bearing ability of the developing roller is greater than that in a developing roller having plural grooves parallel to the rotation axis thereof. Further, a problem in that an undesired horizontal stripe image having a horizontal high-density portion at regular intervals is formed occurs depending on the conditions of the slanting grooves. Furthermore, a problem in that an undesired vertical stripe image having a vertical high density portion at regular intervals is formed occurs depending on the conditions of the slanting grooves.
Because of these reasons, a need exists for a developer bearing member which can maintain its developer bearing ability even after long repeated use without causing the above-mentioned stripe image problems.